> Doesn't mention the 2100 band at all, either PCS or AWS.
AWS is the proper notation, and that's the phrase your looking for when looking for T-Mobile USA phones. When Motorola claims it supports "AWS", they're explicitly telling you that T-Mobile USA HSPA+ works on both bands.
You won't see "1700/2100" often listed on USA phones, specifically because of the problem you just mentioned -- the 2100 band is used unpaired internationally, so it's confusing to see it listed twice, especially when those two uses are completely incompatible.
OK - That's confusing, but it sounds confusing either way. The difference is whether it can only receive on 2100 or also transmit.
Also a bit disappointing, because I'm about to travel to the UK and Europe, and it would be awfully nice to have proper support on all bands. I guess that's another selling point for the Moto X.
When I click that link, I see this for frequency band support:
US GSM Model: GSM/GPRS/EDGE (850, 900, 1800, 1900 MHz) UMTS/HSPA+ up to 21 Mbps (850, 1700 (AWS), 1900 MHz)
Doesn't mention the 2100 band at all, either PCS or AWS. 2100 is only listed for the international model, which lacks the 1700 AWS band.
Is there a link to a more detailed spec sheet?
The Motorola Razr i I am using now works with PCS on T-Mobile, but also explicitly lists the 2100 band, which I believe is required for T-Mobile HSPA+: http://www.gsmarena.com/motorola_razr_i_xt890-4998.php